1. Field of the Invention
The present invention relates to a scroll compressor, and particularly, to a scroll compressor capable of increasing a discharge capacity and freely varying a capacity.
2. Description of the Conventional Art
In general, a compressor is for converting mechanical energy to compression energy of a compressible fluid, and is commonly divided into a reciprocating type, a scroll type, a centrifugal type and a vane type.
Unlike the reciprocating type, the scroll compressor employs a method in which a gas is sucked, compressed and discharged using a rotating body, like the centrifugal or vane compressor.
Such a scroll compressor is commonly applied to an air conditioner. To improve cooling and heating efficiency of the air conditioner, a scroll compressor which can vary its capacity has been recently required.
FIG. 1 is a longitudinal sectional view showing a conventional scroll compressor.
As shown, the conventional scroll compressor includes: a casing 1 provided with a gas suction pipe (SP) and a gas discharge pipe (DP); a main frame 2 and a sub frame (not shown) fixedly installed at upper and lower sides in the casing 1, respectively; a driving motor 3 mounted between the main frame 2 and the sub frame, for generating a rotary force; a rotary shaft 4 fixed at the center of the driving motor 3 and penetrating the center of the main frame 2 for transferring a rotary force of the driving motor 3; a fixed scroll 5 fixedly installed at an upper surface of the main frame 2; an orbiting scroll 6 put on the upper surface of the main frame 2 so as to orbit and engaged with the fixed scroll 5 to form a plurality of compression chambers (P); a self-rotation preventing member 7 (which is called Oldham's ring) installed between the orbiting scroll 6 and the main frame 2, for preventing self-rotation of the orbiting scroll 6 but allowing its orbiting movement; and a discharge cover 8 coupled to an upper surface of the fixed scroll 5 and dividing the inside of the casing 1 into a low pressure portion (S1) and a high pressure portion (S2).
In general, the fixed scroll 8 fixed at an upper portion of the main frame 2 and the orbiting scroll 6 installed between the fixed scroll 8 and the main frame 2 and orbiting are called a compression unit.
A boss receiving pocket 2b for an orbiting movement of a boss portion 6b of the orbiting scroll 6 is formed at a central portion of the main frame 2, and a shaft hole 2a for supporting the rotary shaft 4 is formed at the center of the boss receiving pocket 2b. Key groove portions 2c are formed at both sides of an upper surface of the main frame 2, so that lower key portions 7b of the self-rotation preventing member 7 slide therein in a radial direction.
A wrap 5a forming a compression chamber (P) by being engaged with a wrap 6a of the orbiting scroll 6 to be explained later is formed as an involute shape at a lower surface of the fixed scroll 5. A suction opening 5b is formed at the edgemost of the wrap 5a. And a discharge opening 5c communicating with a high pressure portion (S2) of the casing 1 is formed around the center of the fixed scroll 5.
A wrap 6a is formed as an involute shape at an upper surface of the orbiting scroll 6 and is engaged with the wrap 5a of the fixed scroll 5. And a boss portion 6b coupled to an eccentric portion 4a of the rotary shaft 4 and making an orbiting movement in the boss receiving pocket 2b of the main frame 2 is formed at a central portion of a lower surface of the orbiting scroll 6.
Key groove portions 6c are formed at both sides of the boss portion 6b, so that upper key portions 7c of the self-rotation preventing member 7 slides therein in a radial direction.
As shown in FIG. 2, the self-rotation preventing member 7 includes: a body portion 7a formed as a ring shape; lower key portions 7b formed at both sides of a lower surface of the body portion 7a and slidingly inserted in the key groove portions 2c of the main frame 2; and upper key portions 7c formed at both sides of an upper surface of the body portion 7a and slidingly inserted in the key groove portions 6c of the orbiting scroll 6.
An outer circumferential surface of the body portion 7a is formed as a perfect circle, and sliding surfaces 7d are formed at both sides of its inner circumferential surface. The lower key portions 7b and the upper key portions 7c are alternately formed every angle of 90 along a radial direction.
The operation of the conventional scroll compressor having such a structure will now be described.
When the rotary shaft 4 of the driving motor 3 is rotated by applied power, the orbiting scroll 6 does not self-rotate but makes an orbiting movement by the self-rotation preventing member 7.
At this time, a compression chamber (P) is formed between the wrap portion 6a of the orbiting scroll 6 and the wrap portion 5a of the fixed scroll 5. Then, in the compression chamber (P), a refrigerant gas introduced from the suction opening 5b toward the discharge opening 5c moves toward the discharge opening 5c to be discharged by a constant orbiting movement of the orbiting scroll 6.
Namely, the refrigerant gas is sucked into the low pressure portion (S1) of the casing 1 through the gas suction pipe (SP), and is introduced to the edgemost of the compression chamber (P) through the suction opening 5b of the fixed scroll 5. Then, by a constant orbiting movement of the orbiting scroll 6, the refrigerant gas is compressed, gradually moving inside the compression chamber (P), and is discharged to the high pressure portion (S2) of the casing 1 through the discharge opening 5c of the fixed scroll 5.
However, in the conventional scroll compressor having such a structure, because the refrigerant gas is compressed/discharged only in/from the compression chamber (P) formed by the orbiting scroll 6 and the fixed scroll 5, there is a limit in increasing a capacity of the compressor.
Also, the conventional scroll compressor controls the number of rotation of the driving motor 3 in order to vary a capacity, and should be provided with an expensive controller (not shown) in order to control the capacity, thereby causing an increase in manufacturing cost of the compressor.
In addition, in the conventional scroll compressor, abrasion is badly made between components in a high capacity mode requiring high output, thereby shorting a life span of the compressor, and lubricant oil is not smoothly circulated in the compressor in a low capacity mode requiring low output, thereby degrading compression performance.